The present invention relates to a fuel-vapor emission control system using a charcoal canister for an automotive engine.
There is provided a fuel-vapor emission control system in the automotive engine for preventing air pollution. When the engine operation is stopped, evaporated fuel in a fuel tank and a carburetor is captured and adsorbed by activated charcoal in a charcoal canister of the control system. While the engine is running, the fuel-vapor stored in the canister is purged by intake-manifold vacuum to flow back to the intake system for combustion. A purge control of the canister is provided having a purge control valve provided on the canister which is adapted to be opened by vacuum at a port formed in an intake passage at part throttle operation. The port is positioned just above a throttle valve when it is closed, and hence the fuel-vapor in the canister is delivered together with air into the intake system. Therefore, at starting of a vehicle, when an accelerator pedal is slightly depressed, a large amount of purging takes place. A large amount of vapor by the purging enriches the air-fuel mixture, which will cause the engine to stall.
In order to remove such disadvantages, there is provided a fuel-vapor emission control system for limiting the amount of purging when starting a vehicle. For example, Japanese utility model publication No. 56-54375 discloses a system in which a solenoid operated valve is provided in a purge line and the solenoid is connected in series to a vehicle speed sensor and to a vacuum switch which detects an opening degree of a throttle valve. However, in such a system, purging does not occur at the starting, and it is adapted to take place only at a predetermined vehicle speed. As a result, a decrease of the amount of purging causes an overflow of fuel-vapor from the canister.